Grabner Manfred, ao.Univ.-Prof. Dr.phil.

University / Clinic: Innsbruck Medical University
Institute: Dept of Medical Genetics, Molecular and Clinical Pharmacology
Research Area: Excitation-contraction coupling


Research Topic:
The basic mechanism of coordinated skeletal muscle contraction is the controlled release of Ca2+ from intracellular SR Ca2+ stores. Two distinct Ca2+ channels - the voltage-gated L-type channel or dihydropyridine receptor(DHPR) of the surface membrane and the intracellular Ca2+ release channel or ryanodine receptor (RyR1) of the SR - play together in this complex process called excitation-contraction (EC) coupling. The DHPR thereby senses membrane depolarizations that cause conformational changes of the channel, which, in turn, via protein-protein interaction trigger the opening of RyR1 and thereby the release of SR Ca2+. In addition to this Ca2+-entry-independent orthograde EC coupling signal, a retrograde signal exists in mammalian skeletal muscle, by which RyR1 amplifies the Ca2+ current through the DHPR (= bidirectional coupling).
Our main research topic is to reveal the structure-function relationship of this fascinating bidirectional Ca2+ channel crosstalk. Over the years we succeeded to fine map domains in the cytoplasmic DHPR α1S II-III loop that are essential for this protein-protein signaling interactions with the RyR1, as well as in the α1S C-terminus that are responsible for triad targeting. We found that beside the pore-forming, voltage-sensing α1S subunit, also the accessory DHPR β1a subunit is able to play an essential role in this direct skeletal muscle inter-channel crosstalk by supporting the precise DHPR-RyR co-localization into tetradic arrays. In addition, β1a was identified as the functional switch for EC coupling and intramolecularly cooperating motifs were mapped to the β subunit`s C-terminus and SH3 domain to be responsible for this function. Currently, we are planning to map β1a domains responsible for this interesting DHPR tetrad formation that is so unique for skeletal muscle.
Besides structure-functional domain mapping, our research is devoted to investigate the role of the Ca2+ current through the skeletal muscle DHPR, which is not (directly) involved in skeletal muscle-type EC coupling. Transgenic mouse and zebrafish models play an important role in these projects.

  Structure-function link in the DHPR ß1a subunit for tetrad formation and skeletal muscle motility
details ...

Selected publications:
  Tuluc P, Benedetti B, Costé de Bagneaux P, Grabner M, Flucher B
Two distinct voltage-sensing domains control voltage sensitivity and kinetics of current activation in CaV1.1 calcium channels.
J Gen Physiol. 2016 Jun;147(6):437-49.

  Schrötter K, Dayal A, Grabner M
The mammalian skeletal muscle DHPR has larger Ca2+ conductance and is phylogenetically ancient to the early ray-finned fish sterlet (Acipenser ruthenus).
Cell Calcium. 2016 Oct 23. pii: S0143-4160(16)30163-4. doi: 10.1016/j.ceca.2016.10.002. [Epub ahead

  Dayal A, Bhat V, Franzini-Armstrong C, Grabner M
Domain cooperativity in the β1a subunit is essential for dihydropyridine receptor voltage sensing in skeletal muscle.
Proc Natl Acad Sci U S A. 2013 Apr 30;110(18):7488-93

  Dayal A, Schredelseker J, Franzini-Armstrong C, Grabner M
Skeletal muscle excitation-contraction coupling is independent of a conserved heptad repeat motif in the C-terminus of the DHPR β1a subunit
Cell Calcium. 2010 Jun;47(6):500-6. Epub 2010 May 6

  Schredelseker J, Shrivastav M, Dayal A, Grabner M
Non-Ca2+-conducting Ca2+ channels in fish skeletal muscle excitation-contraction coupling.
Proc Natl Acad Sci U S A. 107(12): 5658-63

  Pirone A, Schredelseker J, Tuluc P, Gravino E, Fortunato G, Flucher B, Carsana A, Salvatore F, Grabner M
Identification and functional characterization of malignant hyperthermia mutation T1354S in the outer pore of the Cavα1S-subunit.
Am J Physiol Cell Physiol 299(6):C1345-54

  Grabner M, Dayal A
Crosstalk via the Sarcoplasmic Gap: The DHPR-RyR Interaction.
Curr Top Membr. 2010;66:115-38.

  Shrivastava M, Schredelseker J, Grabner M
Charged pore residues adjacent to the selectivity filter impede Ca2+ conductivity of the zebrafish DHPR α1S-b
Arch. Biochem. Biophys.; submitted

  Schredelseker J, Dayal A, Schwerte T, Franzini-Armstrong C, Grabner M.
Proper restoration of excitation-contraction coupling in the dihydropyridine receptor β1-null zebrafish relaxed is an exclusive function of the β1a subunit
J Biol Chem. 2009 Jan 9;284(2):1242-51. Epub 2008 Nov 13.

  Bannister R, Grabner M, Beam K
The alpha(1S) III-IV loop influences 1,4-dihydropyridine receptor gating but is not directly involved in excitation-contraction coupling interactions with the type 1 ryanodine receptor (2008)
J Biol Chem., 283; 23217-23123

  Obermair G, Kugler G, Baumgartner S, Tuluc P, Grabner M, Flucher, B
The Ca2+ channel a2d-1 subunit determines Ca2+ current kinetics in skeletal muscle but not targeting of a1S or excitation-contraction coupling.
J. Biol. Chem. 280:2229-2237

  Flucher B, Obermair GJ, Tuluc P, Schredelseker J, Kern G, Grabner M
The role of auxiliary dihydropyridine receptor subunits in muscle.
J Muscle Res Cell Motil. 2005;26(1):1-6. Epub 2005 Oct 14.

  Obermair G, Kugler G, Baumgartner S, Tuluc P, Grabner M, Flucher B
The Ca2+ channel alpha2delta-1 subunit determines Ca2+ current kinetics in skeletal muscle but not targeting of alpha1S or excitation-contraction coupling.
J Biol Chem. 2005 Jan 21;280(3):2229-37. Epub 2004 Nov 9.

  Schredelseker J, Di Biase V, Obermair G, Felder E, Flucher B, Franzini-Armstrong C, Grabner M
The β1a subunit is essential for the assembly of dihydropyridine-receptor arrays in skeletal muscle.
Proc Natl Acad Sci U S A, 102(47): 17219-24

  Kugler G, Weiss R, Flucher B, Grabner M
Structural requirements of the dihydropyridine receptor alpha1S II-III loop for skeletal-type excitation-contraction coupling.
J. Biol. Chem., 279: 4721-4728

  Flucher B, Weiss R, Grabner M
Cooperation of two-domain Ca2+ channel fragments in triad targeting and restoration of excitation-contraction coupling in skeletal muscle.
Proc Natl Acad Sci U S A. 2002 Jul 23;99(15):10167-72

  Koschak A, Reimer D, Huber I, Grabner M, Glossmann H, Engel J, Striessnig J
Alpha1D (Cav1.3) subunits can form L-type Ca2+ channels activating at negative voltages
J Biol Chem, 276: 22100 - 22106

  Wilkens C, Kasielke B, Flucher B, Beam K, Grabner M
Excitation-contraction coupling is unaffected by drastic alteration of the sequence surrounding residues L720-L764 of the alpha1S II-III loop.
Proc. Natl. Acad. Sci. USA, 98, 5892-5897

  Flucher B, Kasielke N, Grabner M
The triad targeting signal of the skeletal muscle calcium channel is localized in the C-terminus of the alpha1S subunit
J. Cell Biol., 151, 467-477